Multi-sheet buffer for compiling print sheets

ABSTRACT

In an apparatus where a printer module outputs print sheets into a finisher module, such as for stapling, a sheet buffer is used to withhold two or more sheets between the printer module and the finisher module so that the finisher module can complete a finishing operation. The withheld sheets are output from the buffer in overlapping fashion when the finisher is ready to accept them. The buffer can be under the control of the printer module or the finisher module.

INCORPORATION BY REFERENCE

[0001] U.S. Pat. No. 5,303,017, assigned to the assignee hereof, ishereby incorporated by reference.

TECHNICAL FIELD

[0002] The present disclosure relates to a buffer for temporarilyretaining sheets, as would be used in a printer or copier, especially inconjunction with a finisher, such as a stapler or folder, which acceptsprint sheets at high speed.

BACKGROUND AND DESCRIPTION OF THE PRIOR ART

[0003] In mid- to high-speed office equipment such as printers andcopiers, the use of “finishers” is well-known. (As used herein, a“copier” will be considered a type of “printer.”) A typical finishingmodule, which may be separable from or integral with the main portion ofthe printer, includes devices for compiling print sheets, such asforming a single multi-page document to be printed, and optionallystapling the compiled sheets. Other known finisher features includefolding, hole-punching, booklet making, etc.

[0004] Many types of actions performed by a finisher require anappreciable amount of time to carry out on a single sheet or on acompiled set of sheets. In the context of a digital printer, however,sheets are ejected from the print engine and accepted by the finisher ata generally regular frequency: in the case of a 60 ppm (page per minute)engine, a sheet is emitted every second; in a 120 ppm engine, a page isemitted every ½ second. A practical problem results when the finisherneeds more time to perform an action than is permitted by the output ofthe engine. Thus, if a finisher requires ¾ of a second to perform afolding or stapling operation, an upstream engine operating at 120 ppmwill emit a next sheet into the finisher while the finisher isperforming the operation, probably resulting in a malfunction of themachine.

[0005] U.S. Pat. No. 5,303,017, incorporated by reference above,discloses a design of what can be called a “sheet buffer,” which isoperatively disposed between a print engine and a finisher. The functionof a sheet buffer is to temporarily withhold a sheet emitted by theprint engine from the finisher for a brief period of time so that thefinisher can perform an action (such as stapling or folding) on one ormore previously-emitted print sheets. In the design shown in the '017patent, a first sheet of interest, to be temporarily withheld, is passedthrough a nip formed by reversible exit rolls. Before the first sheetpasses through the nips, the exit rolls are reversed and the first sheetis “backed up” into a diverter chute, where it is temporarily retained.A second sheet is then caused to move through the exit rollssimultaneously and at least partially overlapping with the first sheet.The output of the buffer is two sheets, which are at least partiallyoverlapping, at once; the effect of the buffer is to temporarilywithhold the sending of the first sheet to the finisher. The buffer ineffect “buys time” for the downstream finisher to perform an action,such as stapling, on previous sheets.

[0006] In the current printing and reprographics industry, it isbecoming common to want to hook up “legacy” finisher modules with newer,ever-faster print engines. In many cases, the print engine output speedis so much greater than the capability of the finisher to accept sheetsthat even withholding a sheet temporarily, as in the '017 patent, doesnot afford the legacy finisher enough time to perform an operationbefore further sheets are forced into it by the print engine.

SUMMARY OF THE INVENTION

[0007] According to one aspect of the present invention, there isprovided method of operating a sheet buffer, the buffer comprising asheet path and a diverter chute communicating with the sheet path, andmeans for moving each of a plurality of sheets through the sheet path.The method comprises moving a first sheet through the sheet buffer in aprocess direction; moving the first sheet in a reverse direction intothe diverter chute; moving a second sheet through the sheet buffer inthe process direction; moving the second sheet in a reverse directioninto the diverter chute; and moving a third sheet through the sheetbuffer in the process direction. The first sheet and second sheet aremoved out of the diverter chute and along the process direction along aportion of the sheet path so that the first sheet, second sheet, andthird sheet at least partially overlap as they exit the sheet path.

[0008] According to another aspect of the present invention, there isprovided a so method of operating a printer module and a finishermechanism. The printer module outputs sheets at a substantially regularbasic speed. A signal is sent, whereby at least a first sheet and asecond sheet output from the printer module are temporarily withheldfrom the finisher mechanism and the first sheet and second sheet areoutput with a third sheet in an overlapping manner, as a result of thesignal.

BRIEF DESCRIPTION OF THE DRAWINGS

[0009]FIG. 1 is an elevational view of the basic hardware associatedwith a sheet buffer.

[0010]FIGS. 2-5 show a series of operations carried out by the basichardware of FIG. 1.

[0011]FIGS. 6 and 7 are simplified elevational views of a high-speedprinter with a finisher module.

DETAILED DESCRIPTION

[0012]FIG. 1 is an elevational view of the basic hardware associatedwith a sheet buffer, generally similar to that disclosed in the '017patent. A main output path such as 12 is disposed, in one embodiment,between a print engine, outputting prints at a regular frequency, and afinisher or other module or mechanism intended to accept print sheets.The output path 12 is defined by upper and lower planar baffles 13 and14. Exit rolls 16, which may be rotated in either direction by means notshown, form a nip at the downstream end of the output path 12, and feedrollers 22 are disposed at the upstream end. Between the exit rollers 16and the upstream feed roller 22 is a diverter gate 24 for diverting asheet being fed upstream by roller 16 into the entrance 32 of a sheetdiverter chute 30 communicating with and branching off at an angle fromthe main output path 12. Within diverter chute 30 are reversible feedrollers 34. All of the rollers and diverters, along with any ancillarysheet position sensors of any type (not shown), can be controlled viaany number of motors or actuators under the control of one or moreprocessors (not shown), in manner generally familiar in the art ofautomated sheet handling.

[0013]FIGS. 2-6 show a series of operations carried out by the basichardware of FIG. 1, according to one embodiment. In the figures, aseries of sheets S1, S2, S3 arrive sequentially at the left of eachFigure, such as if they were being output from a print engine operatingat a basic speed, and then are emitted from the buffer effectively atonce, with the various sheets at least partially overlapping. Theoverlapped multiple sheets can then be accepted by, for example, astapler mechanism within a finisher to the right of the buffer in theFigures.

[0014] In FIG. 2, a first sheet to be emitted, S1, is drawn through theoutput path 12 through the nip of exit rollers 16, through what can becalled a process direction, such as between a print engine and afinisher module. After the trail edge of S1 clears the chute 30, exitrollers 16 are reversed and diverter gate 24 is changed in position,causing S1 to be directed into chute 30 in a reverse direction oppositethe process direction, as shown in FIG. 3. At approximately the sametime, as also shown in FIG. 3, the second sheet to be emitted from theprint engine, S2, is drawn by entrance feed rollers 22 through path 12,with the diverter gate 24 being readjusted at a precise time to clearthe path 12 towards exit rollers 16.

[0015] In FIG. 4, exit rollers 16 are reversed and thus direct S2 towardchute 30, where S1 has remained. At approximately the same time, thethird sheet to be emitted from the print engine, S3, is drawn byentrance feed rollers 22 through path 12, with the diverter gate 24being readjusted at a precise time to clear the path 12 towards exitrollers 16.

[0016] In FIG. 5, exit rollers 16 are rotated (along with rollers 34) toextract sheets S1 and S2, each to some extent overlapping the other,from chute 30 and directing them, along with third sheet S3, togetherthrough exit rollers 16 to a finishing module to the right of the bufferin the Figures. As sheets S1, S2, and S3, pass through exit rolls 16,each sheet to some extent overlaps the others.

[0017] Although the above sequence of operations show a method whichresults in three overlapping sheets being emitted from the buffer, theabove steps can readily be modified, such as by repeating the stepsshown in FIGS. 3 and 4, to cause the buffer to emit four or more sheetsat once.

[0018] For further control of the precise timing of the outputting ofthe sheets S1, S2, and S3 to a finisher, the motion of the exit rollers16 can be finely controlled, such as to momentarily stop (or, morebroadly, momentarily change the speed of) the final output of the sheetsso that the output occurs in a narrowly-defined time window. The precisetiming can be mandated by a control system associated with either aprint engine or a finisher module, as will be described below.

[0019]FIGS. 6 and 7 are simplified elevational views of a high-speedprinter with a finisher module, showing two possible embodiments. Ineither case, a buffer such as shown as sheet path 12 above isoperatively interposed between a printer module 100 and a finishermodule 110. The printer module 100 is controlled by a control system(such as including a microprocessor) 101 and the finisher module 110 iscontrolled by control system 111; the control systems are capable ofcommunicating with each other, so that different finisher modules can bepaired with different printer modules. The printer module 100 typicallyincludes, for example, a paper stack 102 from which blank sheets aredrawn and a print engine such as including a photoreceptor 104 forplacing images on the sheets. The finisher module 110 may include astapler mechanism 112 and an output tray 114, as well as any othermechanism such as for folding, hole punching, booklet making, etc.

[0020] In the FIG. 6 embodiment, the buffer is effectively a part of(that is, is physically disposed in and is controlled by) the printermodule 100. In this way, if a printer module 100 of a predeterminedbasic output speed is linked with a finisher module 110 which is to someextent incapable of accepting sheets at that speed, the control system101 within printer module 100 can be used to operate the hardware suchas shown in FIG. 1 above to temporarily withhold one sheet, or twosheets as in the operations of FIGS. 2-5 above, as needed for thefinisher module 110 to perform a particular action, such as stapling, ata particular time. Depending on the design of the finisher module 110,the overall system can be designed so that control system 101 acceptssome sort of ready signal from control system 111; or if the finishermodule 110 does not have a suitably addressable control system 111, thetemporary withholding of sheets in the buffer can be initiated by thecontrol system 101, such as to follow any stapling command.

[0021] In the FIG. 7 embodiment, the buffer such as including sheet path12 is effectively a part of (that is, is physically disposed in and iscontrolled by) the control system 111 of finisher module 110. In thiscase, when sheets from the printer module 100 are sent into finishermodule 110 at too high a frequency for the finisher module to perform adesired action at a particular time, control system 111 can cause two ormore of the incoming sheets to be temporarily withheld from, forinstance, the stapler mechanism 112, such as when previously-acceptedsheets are being stapled. This temporary withholding of sheets can beinitiated, for example, by an actuation of the stapler or othermechanism 112, and/or by signals received by physical sensors (notshown) indicating the positions of sheets within the module 110.

[0022] The withholding of two or more sheets, within either module 100or 110, enables the print engine within print module 100 to operate at aconstant high speed without having to slow itself down to accommodatethe limitation of a mechanism within finisher module 110. When themechanism such as 112 of finisher module 110 is performing atime-consuming operation, a signal can be sent from finisher controlsystem 111 or printer control system 101, to cause whichever controlsystem is operative of the buffer to initiate the withholding actionsdescribed above, and indeed cause the withholding of more than twosheets as needed until the finisher module is able to accept furthersheets. At the architectural level, the signal to initiate thewithholding of sheets can be designed to originate with the printercontrol system 101 if it is known or suspected that the output speed ofthe printer module 100 is significantly higher than the capability of afinisher module 110 likely to be coupled therewith; conversely, thefinisher control system 111 can originate the signal (even to printercontrol system 101) when it detects or is otherwise instructed thatsheets are being output from printer module 100 faster than isconsistent with an action of the finisher module.

[0023] In another possible embodiment, the printer control system 101can accept a “not ready” signal from the control system 111 of finishermodule 110, and withhold any number of sheets in the buffer accordinglyuntil the finisher module is able to accept further sheets. This use of“ready” or “not ready” signals can be employed even if it is known thata certain finisher action will take a certain amount of time, or inresponse to detected jams or other malfunctions associated with thefinisher module, where it is unknown when the finisher module will beready to accept further sheets.

1. A method of operating a sheet buffer, the buffer comprising a sheetpath and a diverter chute communicating with the sheet path, and meansfor moving each of a plurality of sheets through the sheet path,comprising: moving a first sheet through the sheet buffer in a processdirection; moving the first sheet in a reverse direction into thediverter chute; moving a second sheet through the sheet buffer in theprocess direction; moving the second sheet in a reverse direction intothe diverter chute; moving a third sheet through the sheet buffer in theprocess direction; and moving the first sheet and second sheet out ofthe diverter chute and along the process direction along a portion ofthe sheet path so that the first sheet, second sheet, and third sheet atleast partially overlap as they exit the sheet path.
 2. The method ofclaim 1, further comprising selectably changing a speed of the firstsheet, second sheet, and third sheet as they exit the sheet path.
 3. Themethod of claim 1, further comprising directing the first sheet, secondsheet, and third sheet to a finisher.
 4. The method of claim 1, furthercomprising outputting a signal permitting directing the first sheet,second sheet, and third sheet to the finisher.
 5. The method of claim 4,wherein the signal is sent to a printer control system controlling aprint engine.
 6. The method of claim 1, further comprising moving thethird sheet in a reverse direction into the diverter chute.
 7. A methodof operating a printer module and a finisher mechanism, comprising: theprinter module outputting sheets at a substantially regular basic speed;and sending a signal, whereby at least a first sheet and a second sheetoutput from the printer module are temporarily withheld from thefinisher mechanism and the first sheet and second sheet are output witha third sheet in an overlapping manner, as a result of the signal. 8.The method of claim 7, wherein the signal is sent as a result of anaction of the finisher mechanism.
 9. The method of claim 7, wherein thefinisher mechanism is operated by a finisher control system.
 10. Themethod of claim 9, wherein the signal is sent from the finisher controlsystem to a printer control system operative of the printer module. 11.The method of claim 10, wherein the printer control system is operativeof a buffer which physically withholds the first sheet and the secondsheet.
 12. The method of claim 9, wherein the signal is sent from aprinter control system operative of the printer module to a finishercontrol system operative of the finisher mechanism.
 13. The method ofclaim 9, wherein the finisher control system is further operative of abuffer which physically withholds the first sheet and the second sheet.